Multiple access communication system and data transceiver

ABSTRACT

A multiple access communications system achieving an improvement in transmission efficiency is disclosed. A slave station receives data from variable speed data terminals and generates a plurality of data packets. The slave station then transmits a transmission request packet containing a total amount of data packets to be concatenated to a master station. The master station transmits a transmission permission packet containing a total amount of data packets permitted to be concatenated through a broadcast line to the slave station. The slave station concatenates a plurality of uplink transmission data packets within a predetermined range, and transmits a concatenated uplink transmission data packet to the master station through the multiple access line network.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a multiple access communication systemand a data transceiver used in a broadband access network or the like.

2. Related Art

Broadband access networks such as cable modems using cable televisionlines or Fixed Wireless Access (FWA) using fixed radio channels havebeen provided even in ordinary households to implement high speedinternet access. Cable modems and FWA are described in detail in, forexample, Nikkei Communication, No. 316, April 2000. These broadbandaccess networks nearly all use multiple access lines where a number ofusers share the same frequency band as an uplink, in order to reducecosts. With multiple access type lines, each slave station is connectedto a master station through shared media for sharing the same frequencyband with other slave stations, and a transmission order between slavestations is controlled by master station multiple access control.

In order to synchronize time between the master station and all of theslave stations, the master station distributes a time synchronizationpacket via a broadcast channel. In this type of multiple accesscommunication system, in order to use the uplink efficiently, each slavestation concatenates a plurality of uplink transmission data packets totransmit them. Also, the slave stations separately manage transmissiondata itself and state information representing the state of thetransmission data. When a slave station sets a control flag within thestate information to unchangeable, a MAC (media access control)controller automatically transmits a corresponding transmission databody to the uplink. When concatenating and transmitting, the slavestation sets a concatenated transmission flag in the state information,and the MAC controller consecutively concatenates all transmission databodies having a concatenated transmission flag set and automaticallytransmits them to the uplink.

When transmitting communication data, a conventional multiple accesscommunications system adds additional information to the communicationdata to be transmitted. In the case of concatenating a plurality oftransmission data, additional information for indicating that there isconcatenated data is further added for transmission. By doing this, ifthe size of the additional information becomes large compared to thesize of the transmission data, the concatenating of a plurality oftransmission data for transmission suffers from a first problem thatconversely the utilization rate of the multiple access lines isdegraded.

Also, when a slave station concatenates and transmits a plurality oftransmission data, the uplink is occupied for a long period of time sothere is a second problem that the length of time that other slavestations must wait until transmitting transmission data is increased.

According to a conventional multiple access communication system,generation of transmission data and transmission to the multiple accessline is asynchronous. Accordingly, there is developed a third problemthat a delay in transmission data, which is required in real time, isincreased.

Since transmit packets in a transmission buffer are transmittedautomatically one by one, in order to concatenate and transmittransmission data there is a fourth problem that it is necessary to havecompleted concatenating processing by the time transmission data is putinto the transmission buffer.

The uplink control information and uplink user data make shared use ofthe same transmission buffer, and a slave station sequentially performstransmission from header transmission data in the transmission buffer.Accordingly, there is a fifth problem that the uplink controlinformation is not given priority over the uplink user data whenperforming transmission.

In the case of concatenating a plurality of packets having a fixedinformation length, Japanese Patent Application Unexamined PublicationNo. 61-33054 discloses a packet transmitting/receiving system where astart block is added to the leading end of the concatenated packets andan end block is added to the trailing end thereof. However, this priorart is applicable to a fixed-length packet transmitting/receivingsystem.

SUMMARY OF THE INVENTION

The present invention has been conceived in view of the above describedsituation, and a first object of the present invention is to provide amultiple access communication system and a data transceiver allowingalways highly efficient utilization rates for multiple access lines.

A second object of the present invention is to provide a multiple accesscommunication system and a data transceiver avoiding an uplink to beoccupied by a single slave station for a long period of time.

A third object of the present invention is to provide a multiple accesscommunication system and a data transceiver allowing reduced delay oftransmission data that is required in real time.

A fourth object of the invention is to provide a multiple accesscommunication system and a data transceiver allowing all transmissiondata satisfying concatenated transmission conditions to be concatenatedand transmitted.

A fifth object of the present invention is to provide a multiple accesscommunication system and a data transceiver allowing uplink controlinformation to be transmitted with priority over uplink user data.

In order to achieve the above described objects, a first aspect of thepresent invention is a multiple access communications system including:a master station; and a plurality of slave stations, each of which isconnected to the master station using an uplink and a downlink and isconnected to at least one terminal. Each of the slave stations includes:a transmission buffer for storing data received from a terminal asuplink transmission packets; a condition memory storing a transmissioncondition for packet concatenation; a packet concatenation section forconcatenating a plurality of uplink transmission packets stored in thetransmission buffer within a range satisfying the transmissioncondition, to produce a concatenated uplink transmission packet; and atransmitter for transmitting the concatenated uplink transmission packetto the master station.

The packet concatenation section may concatenate a plurality of uplinktransmission packets within an upper limit to number of uplinktransmission packets determined by the transmission condition. Thepacket assembler may concatenate a plurality of uplink transmissionpackets within an upper limit to a total amount of uplink transmissionpackets determined by the transmission condition.

The transmission condition may be previously set such that concatenatingof the plurality of uplink transmission packets is performed only when atotal amount of first additional information that would be added if theuplink transmission packets are individually transmitted is not smallerthan an amount of second additional information that would be added ifthe concatenated uplink transmission packet is transmitted, wherein thepacket concatenation section concatenates the plurality of uplinktransmission packets when the transmission condition is satisfied.

The slave station may further include a table memory storing a tablecontaining correspondence between a packet data size and an amount ofadditional information to be added when individually transmitted,wherein the table is used to determine whether the total amount of firstadditional information is not smaller than the amount of secondadditional information.

The slave station may further include a table memory storing a tablecontaining correspondence between a packet data size, a number ofpackets to be concatenated, an amount of additional information to beadded when concatenated, and wherein the table is used to determinewhether the total amount of first additional information is not smallerthan the amount of second additional information.

According to another aspect of the present invention, a multiple accesscommunications system includes: a master station; and a plurality ofslave stations, each of which is connected to the master station usingan uplink and a downlink and is connected to at least one fixed speeddata terminal. The master station includes a time synchronization packettransmitter for transmitting a time synchronization packet to the slavestations to obtain time synchronization with the slave stations, andeach of the slave stations includes: a converter for converting allfixed speed data received from the at least one fixed speed dataterminal to uplink transmission data packets in synchronization with thetime synchronization packet, and a transmitter for starting transmissionprocessing of the uplink transmission data packets when the fixed speeddata from all of the at least one fixed speed data terminal have beenstored.

Each of the slave stations may further include: a detector for detectingat least one fixed speed data terminal that is in an active state,wherein the transmitter starts the transmission processing of the uplinktransmission data packets when the fixed speed data from all of the atleast one fixed speed data terminal that is in the active state has beenstored.

The master station may periodically transmit a transmission permissionpacket to the slave stations, wherein the converter converts the fixedspeed data to uplink transmission data packets in synchronism with thetransmission permission packet, and the transmitter performstransmission of the uplink transmission data packets according to timingdesignated by the transmission permission packet.

According to further another aspect of the present invention, a multipleaccess communications system includes: a master station; and a pluralityof slave stations, each of which is connected to the master stationusing an uplink and a downlink and is connected to at least oneterminal, wherein each of the slave stations transmits an uplink datapacket and an uplink control information packet to the master station asan uplink transmission data packet. Each of the slave station includes afirst buffer for storing uplink transmission data packets; a secondbuffer for storing uplink transmission data packet status informationindicating a status of each of the uplink transmission data packets; anda buffer controller controlling such that, when an uplink transmissiondata packet is stored in the first buffer, a control flag is set tonot-changeable and is added to uplink transmission data packet statusinformation corresponding to the uplink transmission data packet, andthe uplink transmission data packet status information with the controlflag set to not-changeable is stored in the second buffer.

The buffer controller may previously set an upper limit to a number ofuplink transmission data packets to be set to not-changeable, wherein,when a number of uplink transmission data packets exceeds the upperlimit, the buffer controller sets the control flag to changeable andadds it to uplink transmission data packet status informationcorresponding to uplink transmission data packets exceeding the upperlimit, to store the uplink transmission data packet status informationwith the control flag set to changeable in the second buffer.

Each of the slave stations may further include a condition memorystoring a transmission condition, wherein, when a number of uplinktransmission data packets set to not-changeable falls below the upperlimit, the buffer controller determines whether the uplink transmissiondata packets set to changeable stored in the first buffer satisfy thetransmission condition, and when the uplink transmission data packetsset to changeable satisfy the transmission condition, the buffercontroller sets a control flag of uplink transmission data packet statusinformation corresponding to each of the uplink transmission datapackets set to changeable to not-changeable, and concatenates the uplinktransmission data packets set to changeable in sequence to produce aconcatenated uplink transmission packet for transmission to the masterstation.

The buffer controller may controls such that, when the uplink controlinformation packet is stored in the first buffer, the uplink controlinformation packet is stored at a location of the first bufferimmediately before the uplink transmission data packets set tonot-changeable stored in the first buffer.

According to the present invention, a data transceiver connected betweena master station and at least one terminal to transfer data between themaster station and the at least one terminal, includes: a transmissionbuffer for storing data received from a terminal as uplink transmissionpackets; a condition memory storing a transmission condition; a packetconcatenation section for concatenating a plurality of uplinktransmission packets stored in the transmission buffer within a rangesatisfying the transmission condition, to produce a concatenated uplinktransmission packet; and a transmitter for transmitting the concatenateduplink transmission packet to the master station.

According to the present invention, a data transceiver connected betweena master station and at least one fixed speed data terminal to transferdata between the master station and the at least one terminal, includes:a packet data generator for generating uplink transmission data packetsfrom fixed speed data received from the at least one fixed speed dataterminal, in synchronization with a time synchronization packet receivedfrom the master station to; and a data packet transmitter for performingtransmission processing of the uplink transmission data packets when thefixed speed data from all of the at least one fixed speed data terminalhave been received.

According to the present invention, a data transceiver connected betweena master station and at least one terminal to transfer data between themaster station and the at least one terminal, includes: a first bufferfor storing uplink transmission data packets; a second buffer forstoring uplink transmission data packet status information indicating astatus of each of the uplink transmission data packets; and a buffercontroller controlling such that, when an uplink transmission datapacket is stored in the first buffer, a control flag is set tonot-changeable and is added to uplink transmission data packet statusinformation corresponding to the uplink transmission data packet, andthe uplink transmission data packet status information with the controlflag set to not-changeable is stored in the second buffer.

According to the present invention, a multiple access communicationmethod between a master station and a plurality of slave stations, eachof which is connected to the master station using an uplink and adownlink and is connected to at least one terminal, includes the stepsof: at a slave stations, generating a plurality of data packets fromdata received from the at least one terminal; transmitting atransmission request packet containing a total amount of data packets tobe concatenated to the master station; at the master station, inresponse to the transmission request packet, transmitting a transmissionpermission packet containing a total amount of data packets permitted tobe concatenated to the slave station; at the slave station,concatenating a plurality of uplink transmission data packets within apredetermined range to produce a concatenated uplink transmission datapacket; and transmitting the concatenated uplink transmission datapacket to the master station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a multiple access communicationsystem employed for explanation of first to sixth, ninth and tenthembodiments of the present invention.

FIG. 2 is a block diagram of a slave station of first, second, third andfourth embodiments of the present invention.

FIG. 3 is a diagram showing an example of the format of an uplinktransmission data packet of the first embodiment of the presentinvention.

FIG. 4 is a diagram showing an example of the format of an uplinktransmission data packet of the second embodiment of the presentinvention.

FIG. 5 is a diagram showing an example of the format of an uplinktransmission data packet of the third embodiment of the presentinvention.

FIG. 6 is a block diagram of a slave station of fourth and fifthembodiments of the present invention.

FIG. 7 is a table regarding size of data packets held in a storagecircuit 380 of FIG. 6 in the fourth embodiment of the presentembodiment.

FIG. 8 is a table regarding number and size of data packets to beconcatenated held in the storage circuit 380 of the fifth embodiment ofthe present invention in FIG. 6.

FIG. 9 is a block diagram of a multiple access communication system ofthe sixth, seventh and eighth embodiments of the present invention.

FIG. 10 is a block diagram of a slave station of the sixth embodiment ofthe present invention.

FIG. 11 is a diagram showing activity of signals at each section of thesixth embodiment of the present invention.

FIG. 12 is a block diagram of a slave station of the seventh embodimentof the present invention.

FIG. 13 is a diagram showing activity of signals at each section of theseventh embodiment of the present invention.

FIG. 14 is a block diagram of a slave station of the eighth embodimentof the present invention.

FIG. 15 is a diagram showing activity of signals at each section of theeighth embodiment of the present invention

FIG. 16 is a block diagram of a slave station of the ninth and tenthembodiments of the present invention.

FIG. 17 is a block diagram showing details of the buffer inside themultiple access line termination circuit of the ninth embodiment of thepresent invention in FIG. 16.

FIG. 18 is a block diagram showing details of the buffer inside themultiple access line termination circuit of the tenth embodiment of thepresent invention in FIG. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

A first embodiment of the present invention will be described in thefollowing, with reference to the drawings.

FIG. 1 is a block diagram showing a multiple access communication systemof this embodiment. In this drawing, a plurality of slave stations 20,21 and 23 receive data and control information from a master station 10through a broadcast line 50. The master station 10 receives data packetsand control information packets from the plurality of slave stationsthrough a multiple access line 60. Also, the slave station 20 isconnected to a variable speed data terminals 30 and 31 through variablespeed communication lines 80 and 81 respectively.

FIG. 2 is a block diagram showing the above-described slave station indetail. A broadcast line termination circuit 200 receives data from themaster station, while a multiple access line termination circuit 210transmits data to the master station. A variable speed communicationline termination circuit 220 transmits and receives data to and from thevariable speed communication terminal, and a variable speed datatransmission buffer 240 holds uplink transmission data from the variablespeed communication terminals. A broadcast line network interface 260receives downlink transmission data packets from the master station 10,and a multiple access line network interface 270 receives uplinktransmission data packets from the slave station 20. Variable speedcommunication network interfaces 280 and 281 perform data communicationwith the variable speed communication terminals.

Next, an operation of the first embodiment will be described. In FIG. 1and FIG. 2, when the variable speed communications terminals 30 and 31transmit data, the variable speed communication network interfaces 280and 281 receive this data, and this data is held in the variable speeddata transmission buffer 240 through the variable speed communicationline termination circuit 220. At this time, the multiple access linetermination circuit 210 references a transmission condition for packetconcatenation being held internally. Only when this transmissioncondition is satisfied, the slave station 20 produces a transmissionrequest packet 360 having its own station number and a total data sizeincluded therein, and transmits it to the master station 10 through themultiple access line network 60. When having received the transmissionrequest packet 360 from the slave station 20, the master station 10produces a transmission permission packet 300 having the number of theslave station 20 and a data size approved for transmission includedtherein and transmits this signal to the slave station 20 via thebroadcast line 50. The slave station 20 receives the transmissionpermission packet 300 at the broadcast line termination circuit 200through the broadcast line network interface 260. Then, the broadcastline termination circuit 200 sends a transmission instruction signal 370containing data size information approved for transmission to themultiple access line termination circuit 210. The multiple access linetermination circuit 210, when having received the transmissioninstruction signal 370, extracts a plurality of transmission dataappropriate for the designated data size from the variable speed datatransmission buffer 240, concatenates the plurality of data within apredetermined range and adds an overhead such as concatenated headerinformation containing information used for separation at the receiveside and physical layer header information such as Forward ErrorCorrection (FEC). After that, the data is sent via the multiple accessline network interface 270 and the multiple access line 60 to the masterstation 10 as an uplink transmission data signal 310.

FIG. 3 is an example of the format of the uplink transmission datapacket signal 310. When transmission data packets 400, 401, 402 and 403of P1, P2, . . . Pn-1, Pn are held in the variable speed datatransmission buffer 240 of the slave station 20, the multiple accessline termination circuit 210 reads out an internally held transmissioncondition. When the transmission condition sets an upper limit to thenumber of concatenated transmission packets, the multiple access linetermination circuit 210 performs concatenating for a number ofconcatenated data packets 440 that is only a number of data packets thatdoes not exceed the upper limit set by the transmission condition. Themultiple access line termination circuit 210 adds a concatenatedtransmission overhead 530 to the concatenated transmission data packets510 and then transmits a resultant signal to the master station 10 viathe multiple access line network 60.

Here, assuming that the upper limit to the number of concatenated datapackets is twenty and twenty-five transmission data packets are held inthe variable speed data transmission buffer 240, twenty ones of thetwenty-five transmission data packets are concatenated, a concatenatedtransmission data packet 510 is generated, a concatenated transmissionoverhead 530 is added and transmission is performed.

Second Embodiment

Next, a second embodiment of the present invention will be describedwith reference to FIG. 1, FIG. 2 and FIG. 4.

FIG. 4 is an example of the format of an uplink transmission data packetaccording to the second embodiment. When uplink transmission datapackets P1, P2, . . . Pn-1, Pn are held in the variable speed datatransmission buffer 240, the multiple access line termination circuit210 reads out an internally held transmission condition. When an upperlimit value for a concatenated data packet size has been set in thetransmission condition, the multiple access line termination circuit 210performs concatenating for only a concatenated data packet size 430 thatdoes not exceed the upper limit value, adds a concatenated transmissionoverhead 530 to the concatenated transmission data packet 510 andtransmits a resultant packet to the master station 10 through themultiple access line network 60.

For example, assuming that the upper limit to the concatenated datapacket size is 1100 bytes and the variable speed data transmissionbuffer 240 holds a total of five uplink transmission data packets:P1=100 bytes, P2=200 bytes, P3=300 bytes, P4=400 bytes and P5=500 bytes,uplink transmission data packets P1 to P4 are concatenated, and themultiple access line termination circuit 210 generates a 1000-byteconcatenated transmission data packet 510.

Third Embodiment

Next, a third embodiment of the present invention will be described withreference to FIG. 1, FIG. 2 and FIG. 5.

FIG. 5 is an example of the format of an uplink transmission data packetof this third embodiment. When uplink transmission data packets 400,401, 402 and 403 shown as P1, P2, . . . Pn-1, Pn are held in thevariable speed data transmission buffer 240, the multiple access linetermination circuit 210 reads out a transmission condition for packetconcatenation. Processing is set for the case where a concatenatedtransmission overhead size meeting the transmission condition is smallerthan the total size of individual transmission overheads.

In the case of individual transmission, transmission overheads 520, 521,522 and 523 shown as H1, H2 . . . Hn are individually added to uplinktransmission data packets 400, 401, 402 and 403 and are transmitted.Also, in the case of concatenated transmission, the uplink transmissiondata packets 400, 401, 402 and 403 are transmitted as a concatenatedtransmission data packet 510 having a concatenated transmission overhead530 added thereto. Here, a sum Hsum of the sizes of the overheads H1, H2. . . Hn at the time of each individual transmission is compared withthe size of the concatenated transmission overhead 530. The concatenatedtransmission is only carried out when the size of the concatenatedtransmission time overhead 530 is smaller than the sum Hsum of the sizesof the individual transmission overheads.

For example, it is assumed that a 10-byte overhead is added if uplinkdata packets are sent individually using the multiple access linenetwork 60 and that a 15-byte overhead is added if transmitting aconcatenated data packet. With this embodiment when a 500-byte uplinkdata packet A and a 100-byte uplink data packet B are held in thevariable speed data transmission buffer 240, with individualtransmission an uplink data packet of a total of 620 bytes, that of twouplink data packets of 510 bytes and 110 bytes, each having a 10-byteoverhead added, is generated. On the other hand, with concatenatedtransmission, a data packet having a total of 615 byes, that of the600-byte concatenated transmission data packet with a 15-byte overheadadded, is generated. Accordingly, since the method of concatenatedtransmission has a smaller overhead size compared to the individualtransmission, transmission data A and B are concatenated andtransmitted.

Fourth Embodiment

Next, a fourth embodiment of the present invention will be describedwith reference to FIG. 1, FIG. 6 and FIG. 7.

FIG. 6 shows the structure of a slave station 20 according to the fourthembodiment. In this embodiment, a memory circuit 380 holds an overheadsize correspondence table. Here, a transmission condition for packetconcatenation is set such that, when an overhead size for concatenatedtransmission is smaller than the total size of overheads for individualtransmission, the multiple access line termination circuit 210concatenates transmission data packets.

FIG. 7 shows an example of the overhead size correspondence table beingstored in the memory circuit 380 of the slave station 20 as shown inFIG. 6. The multiple access line termination circuit 210 inside theslave station 20 notifies a data packet size to the memory circuit 380using the control signal 390 when transmitting a plurality of uplinktransmission data packets being held in the variable speed datatransmission buffer 240. In response to the data packet size, the memorycircuit 380 searches the individual transmission overhead sizecorrespondence table 600 (FIG. 7) for a corresponding overhead size andoutputs the found overhead size back to the multiple access linetermination circuit 210 via the control signal 390. The multiple accessline termination circuit 210 compares the total overhead size calculatedfrom the overhead sizes found in the table 600 with a concatenatedtransmission overhead that is calculated separately, and performsconcatenated transmission only if the overhead size is smaller for theconcatenated transmission than for the individual transmission.

Fifth Embodiment

Next, a fifth embodiment of the present invention will be described withreference to FIG. 1, FIG. 6 and FIG. 8.

FIG. 8 shows an example of an overhead size correspondence table held inthe memory circuit 380 of the slave station 20 as shown in FIG. 7. Themultiple access line termination circuit 210 inside the slave station 20notifies the number of data packets and the size of the data packets tothe memory circuit 380 using the control signal 390 when transmitting aplurality of uplink transmission data packets being held in the variablespeed data transmission buffer 240. In response to the number of datapackets and the data packet size, the memory circuit 380 searches theconcatenated transmission overhead size correspondence table 700 (FIG.8) for a corresponding overhead size and outputs the found overhead sizeback to the multiple access line termination circuit 210 via the controlsignal 390. The multiple access line termination circuit 210 comparesthe concatenated transmission overhead size received from the memorycircuit 380 with the total overhead size that is separately calculated,and performs concatenated transmission only if the overhead size issmaller for the concatenated transmission than for the individualtransmission.

Sixth Embodiment

Next, a sixth embodiment of the present invention will be described withreference to FIG. 9, FIG. 10 and FIG. 11.

FIG. 9 shows a multiple access communication system of the sixthembodiment. A master station 10 and a plurality of slave stations 20, 21and 22 are connected through distributors 70 and 71. Data and controlinformation are sent from the master station 10 to the plurality ofslave stations 21, 21 and 22 using a broadcast line 50. Data packets andcontrol information are sent from the plurality of slave stations 20, 21and 22 to the master station 10 using the multiple access line 60. Also,the slave station 20 is connected to respective fixed speed dataterminals 40, 41 and 42 via fixed speed communication lines 90, 91 and92.

FIG. 10 shows the structure of the slave station 20 according to thesixth embodiment. When all of the fixed speed data terminals 40, 41 and42 are in an active state, first of all if three fixed speed datasignals 330, 331 and 332 are received, sampling is carried in the fixedspeed communication line termination circuit 230 of the slave station20, using a signal obtained by dividing a time synchronization packet393 that is provided through the broadcast line 50 in order to obtaintime synchronization of the master station 10 with the slave stations20, 21 and 22. Then, all of the input fixed speed data signals 330, 331and 332 are transferred to the fixed speed data transmission buffer 250inside the multiple access line termination circuit 210 as fixed speeddata packets 800, 801 and 802 (see FIG. 11). When all of the fixed speeddata packets 800, 801 and 802 are accumulated in the fixed speed datatransmission buffer 250, the multiple access line termination circuit210 produces a transmission request packet 360 having its own stationnumber and a total data size included therein, and transmits it to themaster station 10 through the multiple access line network 60. Themaster station 10 that has received the transmission request packet 360produces a transmission permission packet 300 having the slave stationnumber and a data size permitted to be transmitted included therein andtransmits it to the slave station 20 via the broadcast line 50. Whenreceiving the transmission permission packet 300 at the broadcast linetermination circuit 200, a transmission instruction signal 370containing information for data permitted for transmission istransferred to the multiple access line termination circuit 210.

The multiple access line termination circuit 210 that has received thetransmission instruction signal 370 extracts a plurality of transmissiondata packets corresponding to the designated data size from the fixedspeed data transmission buffer 250, concatenates the extracted datapackets and attaches an overhead such as FEC thereto. After that, theconcatenated data is transmitted to the master station 10 as atransmission data signal 310 through the multiple access line 60.

FIG. 11 shows processing of a signal at each section of the abovedescribed embodiment. After carrying out sampling of the fixed speeddata signals 330, 331 and 332 in the fixed speed communication linetermination circuit 230 of the slave station 20 using a signal dividedfrom a time synchronization packet, respective fixed speed data packets800, 801 and 802 are generated. The fixed speed data packets 800, 801and 802 are sent to the fixed speed data transmission buffer 250. Uponcompletion of receipt of all fixed speed data packets, the multipleaccess line termination circuit 210 requests concatenated transmissionto the master station 10 using the transmission request packet 360. Themaster station 10 gives permission for this concatenated transmissionand notifies the slave station 20 using the transmission permissionpacket 300. In the event that performing concatenated transmissionsatisfies the transmission conditions, the multiple access linetermination circuit 210 of the slave station 20 concatenates all of thefixed speed data packets 800, 801 and 802 to create a concatenatedtransmission data packet 510, adds to this a concatenated transmissionoverhead 530 and transmits a resultant packet as a transmission datasignal 310 to the master station 10 through the multiple access linenetwork 60.

Seventh Embodiment

Next, a seventh embodiment of the present invention will be describedwith reference to FIG. 9, FIG. 12 and FIG. 13.

FIG. 12 shows a slave station of this embodiment. In FIG. 12, an activestation detection circuit 391 detects whether or not the fixed speeddata terminal is in an active state. FIG. 13 shows processing of asignal at each section of this seventh embodiment.

In FIG. 9, FIG. 12 and FIG. 13, the fixed speed communication linetermination circuit 230 of the slave station 20 has the active statedetection circuit 391 inside, and in the active state detection circuit391 it is detected whether or not all fixed speed data terminals 40, 41and 42 connected to the slave station 20 are in an active state. In theexample shown in FIG. 13, two fixed speed data terminals 40 and 41 arein an active state. The number of fixed speed data terminals that are inthe active state is notified to the multiple access line terminationcircuit 210 using an active state notification signal 392. The multipleaccess line termination circuit 210 receiving this notification receivesthe fixed speed data packets 800 and 801 from the two fixed speed dataterminals 40 and 41. When concatenating and transmitting satisfies thetransmission condition, concatenating and transmitting of these two datapackets is requested to the master station 10 using a transmissionrequest packet 360. When the master station 10 permits this action andnotifies the slave station 20 of transmission permission using thetransmission permission packet 300, the broadcast line terminationcircuit 200 of the slave station 20 receives the transmission permissionpacket 300 and transfers a transmission instruction signal to themultiple access line termination circuit 210. The two fixed speed datapackets 800 and 801 are then concatenated in the multiple access linetermination circuit 210, a concatenated transmission data packet 510 ismade, and a concatenated transmission overhead 530 is added thereto, andthen transmitted to the master station 10 as a transmission data signal310 via the multiple access line network 60.

Eighth Embodiment

Next, an eighth embodiment of the present invention will be describedwith reference to FIG. 9, FIG. 14 and FIG. 15.

FIG. 14 shows a slave station 20 of this eighth embodiment, while FIG.15 is a drawing showing processing of a signal at each section of thisembodiment.

In FIG. 9, FIG. 14 and FIG. 15, in the event that only the fixed speeddata terminal 40 connected to the slave station 20 is in an activestate, the master station 10 periodically transmits the transmissionpermission packet to the slave station 20. When the broadcast linetermination circuit 200 receives the transmission permission packet 300from the master station 10, a synchronization pulse 900 is sent to thefixed speed data communication line termination circuit 230 as atransmission synchronization signal 394 in compliance with transmissiontiming of the multiple access line termination circuit 210, and thefixed speed data communication line termination circuit 230 produces afixed speed data packet 800 synchronized to the synchronization pulsesignal 900 and sends it to the fixed speed data transmission buffer 250within the multiple access line termination circuit 210. The multipleaccess line termination circuit 210 produces a transmission requestpacket having its own station number and a total data size includedtherein and transmits this transmission request packet to the masterstation 10 through the multiple access line 60. The master station 10that has received the transmission request packet 360 produces atransmission permission packet 300 having the number of the slavestation 20 and a data size permitted to be transmitted included thereinand sends it to the slave station 20 via the broadcast circuit 50. Whenthe broadcast line termination circuit 200 of the slave station 20 hasreceived the transmission permission packet 300, it is transferred tothe multiple access line termination circuit 210 as a transmissioninstruction containing data information for permitting transmission. Themultiple access line termination circuit 210 adds an individualtransmission overhead 520 to the fixed speed data packet 800 produced insynchronism with the aforementioned master station, and transmits aresultant packet to the master station 10 as a transmission data signal310 via the multiple access line 60.

Ninth Embodiment

Next, a ninth embodiment of the present invention will be described withreference to FIG. 1, FIG. 16 and FIG. 17.

FIG. 16 shows a slave station of this ninth embodiment. The slavestation 20 has a control circuit 1000, while the multiple access linetermination circuit 210 has an uplink status information buffer 1100 andan uplink data transmission buffer 1110.

When the multiple access line termination circuit 210 has received avariable speed data packet signal 340 from the variable speedcommunication line termination circuit 220, this signal is stored in theuplink data transmission buffer 1110 as uplink transmission data packet1030. When the multiple access line termination circuit 210 has receivedan uplink control information packet signal 1010 from the controlcircuit 1000, this signal is stored as an uplink control informationpacket 1020 in the uplink transmission buffer 1110. In this way, whenthe uplink transmission data packet 1030 is stored in the uplinktransmission buffer 1110, the multiple access line termination circuit210 produces uplink transmission data packet status information 1050.Also, when an uplink control information packet 1020 is stored in theuplink data transmission buffer 1110, the multiple access linetermination circuit 210 produces uplink control information packetstatus information 1040. The uplink transmission data packetstatus-information 1050 and uplink control information packet statusinformation 1040 are held in the uplink status information buffer 1100.The respective uplink transmission data packet status information 1050and uplink control information packet status information 1040 havecontrol flags therein. Either not-changeable or changeable is set ineach control flag, and the number of uplink transmission data packetsthat can be set to not-changeable has an upper limit value.

FIG. 17 shows the detailed structure of the uplink status informationbuffer 1100 and the uplink data transmission buffer 1110.

It is assumed that the upper limit value for the number of data packetsthat can be stored in each of the uplink status information buffer 1100and the uplink data transmission buffer 1110 is made to be 2. In FIG.17, reference numerals 1140, 1141, and 1150 to 1155, denote uplinktransmission data packets. Reference numerals 1120, 1121 and 1130 to1135 denote uplink transmission data packet status informationcorresponding to the uplink transmission data packets 1140, 1141 and1150 to 1155. Control flags of the uplink transmission data packetstatus information 1120 and 1121 are not changeable. Control flags ofthe uplink transmission data packet status information 1130 and 1135 arechangeable.

It is assumed that the uplink data transmission buffer 1110 is empty.The two uplink transmission data packets 1140 and 1141 are respectivelyheld at A1 and B1 in the uplink data transmission buffer 1110. At thistime, the multiple access line termination circuit 210 produces twouplink transmission data packet status information 1120 and 1121corresponding respectively to the uplink transmission data packets 1140and 1141. Control flags of the uplink transmission data statusinformation 1120 and 1121 are set to be not-changeable. At this time,the multiple access line termination circuit 210 respectively holds theuplink transmission data packet status information 1120 and 1121 at A2and B2 in the uplink status information buffer 1100. In the case wherethe slave station 20 has received more uplink transmission data packets,the multiple access line termination circuit 210 holds uplinktransmission data packets 1150 to 1155 at Cl to H1 in the uplinktransmission data buffer 1110. At this time, the multiple access linetermination circuit 210 produces uplink transmission data packet statusinformation 1130 to 1135 respectively corresponding to the uplinktransmission data packets 1150 to 1155. Control flags of the uplinktransmission data packet status information 1130 to 1135 are set to bechangeable. These uplink transmission data packet status information1130 to 1135 are respectively held at C2 to H2 in the uplink statusinformation buffer 1100.

In the above described status denoted by “S”, the slave station 20transmits the transmission request packet 360 to the master station 10.The master station 10 receives this transmission request packet 360 andtransmits a transmission permission packet 300 to the slave station.When the slave station 20 receives permission for transmission, themultiple access line termination circuit 210 extracts the uplinktransmission data packet 1140 from A1 in the uplink transmission datapacket buffer 1110. The multiple access line termination circuit 210adds a transmission request packet for transmitting the next uplinktransmission data packet 1141 to the uplink transmission data packet1140, and transmits it to the master station. At this time, the multipleaccess line termination circuit 210 deletes the uplink transmission datapacket status information A2 from the uplink status information buffer1100. This causes the number of not-changeable uplink transmission datastatus information to be lower than the upper limit value to the numberof data packets that can be stored in each of the uplink statusinformation buffer 1100 and the uplink data transmission buffer 1110.

Subsequently, the transmission condition stored in the multiple accessline termination circuit 210 are referenced. If concatenating andtransmitting of all uplink transmission data packets 1150 to 1155 havinga changeable control flag satisfies the transmission condition, then themultiple access line termination circuit 210 performs concatenatingprocessing, and changes control flags of all uplink transmission datapacket status information 1130 to 1135 having changeable control flagscorresponding to these uplink transmission data packets 1150 to 1155 tonot-changeable.

Tenth Embodiment

Next, a tenth embodiment of the present invention will be described withreference to FIG. 1, FIG. 16 and FIG. 18.

FIG. 18 shows the detailed structure of the uplink status informationbuffer 1100 and the uplink data transmission buffer 1110. Similarly tothe ninth embodiment, an upper limit to the number of data packets thatcan be stored in the uplink status information buffer 1100 and theuplink transmission data packet buffer 1110 is made 2. Reference numeral1190 indicates an uplink control information packet, and referencenumeral 1180 indicates uplink control information packet statusinformation corresponding to uplink control information packet Z2.

At the time of the previously described status S, the multiple accessline termination circuit 210 inserts the uplink control informationpacket 1190 into Z1 immediately before C1 to H1. Next, the multipleaccess line termination circuit 210 produces uplink control informationpacket status information 1180 from the uplink control informationpacket 1190. The multiple access line termination circuit 210 theninserts the uplink control information packet status information 1180into Z2 immediately before C2 to H2. In this manner, the uplink controlinformation packet 1190 can be transmitted with taking precedence overuser data packets.

The ten embodiments of the present invention have been described above,but the present invention is not limited to these embodiments, andvarious modifications are possible within the scope of the presentinvention. For example, in all of these embodiments, the master stationand the slave stations are connected by a wired network, but it is alsopossible to apply the present invention to the case where they areconnected using a wireless network.

As has been described above, according to the present invention, thesize of overheads to be added is compared between concatenatedtransmission and individual transmission, and concatenated transmissionis performed only if the size of the overhead for the concatenatedtransmission case is smaller than for the individual transmission case.This has the effect of always being able to achieve improvement in thetransmission efficiency of a multiple access line network.

Also, when concatenating a plurality of packets for transmission, atransmission condition for packet concatenation is referred to and aplurality of packets is concatenated and transmitted only when atransmission condition for packet concatenation is satisfied.Accordingly, it is possible to prevent a slave station from transmittinga large amount of concatenated packet data over a long period of time,which means that in a multiple access line network, the effect isobtained of preventing a single base station being active over aprolonged period of time and occupying the uplink.

Further, it is possible for a slave station to periodically transmitdata packets due to the master station periodically sending atransmission permission packet and the slave station produces fixedspeed data packets in synchronism with timing at which data packettransmission is permitted. Accordingly, it is possible to shorten thewaiting time for a transmission buffer within the slave station, andthus obtain the effect of making it possible to reduce a delay time forfixed speed data required in real time, such as a telephone.

Further, in a state where a control flag in uplink transmission datapacket status information produced when storing uplink transmission datapackets in the transmission buffer is set to changeable, the uplinktransmission data packet status information is held in the uplink statusinformation buffer. Accordingly, the effect is obtained of enablingconcatenating of a plurality of uplink transmission data packets even inthe case where uplink transmission data packets in the transmissionbuffer are automatically transmitted.

Also, since an uplink control information is inserted into immediatelybefore all uplink user data having the control flag set to changeable inthe transmission buffer, the effect is obtained of making it possible toprioritize transmission of uplink control information compared to theuplink user data.

1-9. (canceled)
 10. A multiple access communications system comprising:a master station; and a plurality of slave stations, each of which isconnected to the master station using a multiple access controlleduplink and a broadcasting downlink and is connected to at least oneterminal, wherein each of the slave stations transmits an uplink datapacket and an uplink control information packet to the master station asan uplink transmission data packet, wherein each of the slave stationcomprise: a first buffer for storing uplink transmission data packets; asecond buffer for storing uplink transmission data packet statusinformation indicating a status of each of the uplink transmission datapackets; and a buffer controller controlling such that, when an uplinktransmission data packet is stored in the first buffer, a control flagis set to not-changeable and is added to uplink transmission data packetstatus information corresponding to the uplink transmission data packet,and the uplink transmission data packet status information with thecontrol flag set to not-changeable is stored in the second buffer. 11.The multiple access communication system according to claim 1, whereinthe buffer controller previously sets an upper limit to a number ofuplink transmission data packets to be set to not-changeable, wherein,when a number of uplink transmission data packets exceeds the upperlimit, the buffer controller sets the control flag to changeable andadds it to uplink transmission data packet status informationcorresponding to uplink transmission data packets exceeding the upperlimit, to store the uplink transmission data packet status informationwith the control flag set to changeable in the second buffer.
 12. Themultiple access communication system according to claim 2, wherein eachof the slave stations further comprises a condition memory storing atransmission condition for packet concatenation, wherein, when a numberof uplink transmission data packets set to not-changeable falls belowthe upper limit, the buffer controller determines whether the uplinktransmission data packets set to changeable stored in the first buffersatisfy the transmission condition, and when the uplink transmissiondata packets set to changeable satisfy the transmission condition, thebuffer controller sets a control flag of uplink transmission data packetstatus information corresponding to each of the uplink transmission datapackets set to changeable to not-changeable, and concatenates the uplinktransmission data packets set to changeable in sequence to produce aconcatenated uplink transmission packet for transmission to the masterstation.
 13. The multiple access communication system according to claim1, wherein the buffer controller controlling such that, when the uplinkcontrol information packet is stored in the first buffer, the uplinkcontrol information packet is stored at a location of the first bufferimmediately before the uplink transmission data packets set tonot-changeable stored in the first buffer. 14-15. (canceled)
 16. A datatransceiver connected between a master station and at least one terminalto transfer data between the master station and the at least oneterminal, comprising: a first buffer for storing uplink transmissiondata packets; a second buffer for storing uplink transmission datapacket status information indicating a status of each of the uplinktransmission data packets; and a buffer controller controlling suchthat, when an uplink transmission data packet is stored in the firstbuffer, a control flag is set to not-changeable and is added to uplinktransmission data packet status information corresponding to the uplinktransmission data packet, and the uplink transmission data packet statusinformation with the control flag set to not-changeable is stored in thesecond buffer. 17-18. (canceled)
 19. A method for transferring databetween a master station and at least one terminal, comprising the stepsof: storing uplink transmission data packets in a first buffer; storinguplink transmission data packet status information indicating a statusof each of the uplink transmission data packets in a second buffer; whenan uplink transmission data packet is stored in the first buffer,setting a control flag to not-changeable and adding it to uplinktransmission data packet status information corresponding to the uplinktransmission data packet; and storing the uplink transmission datapacket status information with the control flag set to not-changeable inthe second buffer. 19-25. (canceled)